1. Field of the Invention
The present invention relates to an electronic apparatus used in a computer system, or the like.
2. Description of the Related Art
A computer system comprises an arithmetic operation section with integrated arithmetic circuits, a cache section operating at a high speed, for processing instructions and data, so as not to reduce the processing capacity of the arithmetic operation section, a memory section for storing the instructions and data sent to the cache section, and peripheral units for reading programs and data from the memory. Also, a system having a plurality of arithmetic operation sections for concurrent operation comprises a common memory section accessible by a plurality of arithmetic operation sections. Especially, the arithmetic operation section and the cache section operate at a high clock frequency in order to improve the operating speed, and involve considerable data changes for large power consumption and heat generation.
Means for cooling these circuits include natural air cooling, forced air cooling, liquid cooling, immersion cooling, etc. Natural air cooling is low in cooling capacity and used for small computers which generate a small amount of heat. Forced air cooling and liquid cooling are used for computers having a high processing capacity. The main application of immersion cooling is to special computers, in test stages, using the Josephson device or the like.
The mainframe computer, as shown in FIG. 47, has a large arithmetic operation circuit, which is configured of a motherboard 201 having a plurality of LSIs 203 mounted thereon. This motherboard generates so much heat that it is cooled by a cooling plate which, in turn, is cooled by a cooling liquid. The cooling plate 206 includes bellows 207 on the portion thereof in opposed relation to the LSIs 203 which generate heat. These bellows 207 are brought into contact with the LSIs 203 to cool the latter. The refrigerant used for this cooling plate 206 is cooled down to about room temperature by a heat exchanger (not shown). The refrigerant absorbs the heat of the LSIs 203 and returns to a heat exchanger not shown. Also, the bellows 207 have a spring property to closely contact the LSIs 203, so that the LSIs 203 and the bellows 207 can thermally contact each other simply by mounting the cooling plate 206 at a predetermined position on the motherboard 201.
This apparatus has LSIs 203 mounted on the two sides of the motherboard 201, though not shown, in order to improve the package density. In order to cool the LSIs 203 mounted on the two sides, two cooling plates 206 are arranged on both sides of the motherboard 201. As a result, when the motherboard develops an abnormality or the requirement for replacement occurs due to the version up of hardware, it is necessary to remote the cooling plate 206 from the housing and then remove the motherboard 201.
Also, with the improvement in the performance of this apparatus and with the increase in the processing capacity of the LSI 203, more heat is generated. To increase the flow rate of the cooling water, however, a lower pressure resistance in the cooling plate, piping, etc. is required. However, the cooling plate, or the like, is arranged in a limited space and it is impossible to increase the size. If the temperature of the cooling water is decreased below room temperature, on the other hand, water drips attach to the motherboard, thereby causing a malfunction. The area at which the motherboard 201 and the cooling plate 206 are thermally connected to each other is limited to the contact area between the LSIs 203 and the bellows 207. To increase this area, a total change of the apparatus structure is required and this is difficult. For improving the cooling performance, therefore, the thermal resistance at the contact surface must be decreased. If the bellows 207 is pressed against the LSIs 203 with a greater force, the LSIs 203 and the motherboard 201 would be damaged. Also, a larger force would be required for mounting the cooling plate 206 for deteriorated maintainability. In view of this, a metal of low melting point is held between the LSIs 203 and the bellows 207 and melted to mount and demount the cooling plate. In this way, the contacting force is increased for a reduced thermal resistance.
As a result, each time the motherboard is replaced or the cooling plate is mounted or demounted, the bothersome labor of spraying hot air higher in temperature than the melting point of the metal between the motherboard and the cooling plate is required for a very deteriorated maintenance efficiency.
With the advance in CMOS techniques, the present-day mainframe computer uses forced air cooling using radiation fins 204, as shown in FIG. 48. A circuit as large as the arithmetic operation circuit mounted on the motherboard 201 in FIG. 47 is formed of one chip by the recently-developed micromachining technology. Thus, the arithmetic operation circuit which has conventionally been configured of a plurality of motherboards is now formed of a single multi-chip module 202. Further, the reduced size of the circuit has shortened the signal line and operation with higher clock frequency is made possible. At the same time, the power saving unique to the CMOS technique eliminates the need for liquid cooling. In this way, the operation capacity of each motherboard 201 has been remarkably improved while the conversion of the cooling method from liquid cooling to forced air cooling has improved the maintenance efficiency.
The change in cooling method from liquid cooling to forced air cooling has eliminated the need of installing the cooling plate and makes it possible to replace the motherboard directly. Also, since there is no need of piping work, the radiation fins can be divided into small units on the motherboard, and the radiation fin can be installed on each multi-chip module constituting a unit of parts on the motherboard. As a result, the multi-chip module can be handled with the radiation fin mounted thereon, and parts can be replaced without removing the cooling plate or the motherboard.
Even with the recent technological development, however, the reduction in circuit size and the operation at a high clock frequency due to the reduced circuit size have reached a limit. As disclosed in JP-A-1-318295, it is known that a semiconductor device can operate at a higher rate of reaction and a higher clock frequency, when the temperature thereof is lower. It is, therefore, unavoidable to introduce such a technique for meeting the prevailing requirement of the processing performance. The technique of cooling the semiconductor devices, which generally includes natural air cooling, forced air cooling and liquid cooling, is the one for preventing the thermal breakdown due to the heat generated in the semiconductor itself. Immersion cooling, on the other hand, which is used for cooling the Josephson device or the like, is realized as a cooling method for maintaining the operating temperature of the device, but the application of this technique to computers in general is difficult due to the maintenance problem.
The object of the present invention is to provide a practical cooling structure, taking maintainability into consideration, in which a semiconductor circuit is cooled to its operating temperature adapted for operation at a high clock frequency.
An electronic apparatus according to this invention comprises a motherboard, multi-chip modules mounted to the motherboard, cooling members for cooling the multi-chip modules, a refrigeration unit for cooling the cooling members to the room temperature or lower, and a connection structure provided for each multi-chip module for thermally and mechanically releasibly coupling each multi-chip module to the refrigeration unit.
The cooling members can be mounted and dismounted while the multi-chip modules are being mounted to the motherboard. As a result, the motherboard can be easily separated from the cooling members, and thereby a cooling structure is realized which secures a sufficient maintainability. Also, in the case where the number of multi-chip modules is increased or decreased depending on the system configuration, the cooling members can be selectively arranged easily for a highly practicable configuration.
The following features can be added to the configuration described above.
The cooling member is fixed to the heat radiating member mounted to the multi-chip module by a fixing member (a screw, for example). Therefore, the electronic element can be cooled positively with the cooling member in close contact with the heat radiating member. By releasing the fixing member (a screw, for example), the cooling member and the multi-chip module can be mechanically separated without considering the troublesome leakage of the cooling water which may otherwise occur in the liquid cooling.
The cooling members are collectively and floatingly supported by a cooling member holding mechanism. In the case where the cooling member is fixed to the heat radiating member by a fixing member (a screw, for example), therefore, the displacement between the cooling member and the heat radiating member is guaranteed. Also, when a plurality of the cooling members are moved away from and toward the heat radiating member, the job can be accomplished in a single operation of moving the cooling member holding mechanism. The maintenance work, therefore, can be done simply by operating the cooling member holding mechanism, thus realizing a cooling mechanism very high in maintainability for the motherboard and the multi-chip module.
The cooling member has a refrigerant inlet, a refrigerant outlet, and a refrigerant path extending between the refrigerant inlet and the refrigerant outlet to circulate the refrigerant at lower than the room temperature. The multi-chip module can thus be cooled efficiently.
The cooling member holding mechanism, together with a plurality of the cooling members, can be moved toward or away from the motherboard. In this case, the cooling member holding mechanism is wholly movable along a slide mechanism. In the maintenance work to be performed on the multi-chip module, therefore, the electronic element mounted on the motherboard is exposed by pulling out the cooling member holding mechanism along the slide mechanism and rotating it like a door.
The cooling member holding mechanism includes a movable portion formed to move, together with each cooling member, toward or away from the motherboard. When the maintenance work is performed on a single multi-chip module, for example, the particular multi-chip module can be exposed by opening only one movable portion of the cooling member holding mechanism.
The multi-chip module is mounted on the motherboard by a connector, and the movable portion of the cooling member holding mechanism is configured to operate in coordination with the connector removing means. By doing so, at the time of maintenance work on a single multi-chip module, the particular multi-chip module can be released from the motherboard by opening only one movable portion of the cooling member holding mechanism.
The multi-chip module is a common board on which a multiplicity of connecting pins for connecting the motherboard and a plurality of semiconductor chips are mounted. A cooling member is mounted on the other side of the board to provide the cooling performance. This multi-chip module is formed for each set of arithmetic operation circuits. In realizing a computer system comprising eight arithmetic operation circuits in parallel, for example, eight multi-chip modules may be mounted on the motherboard.
The connection structure includes, for example, a coupler arranged at the refrigerant inlet and the refrigerant outlet of the cooling member. In this way, the cooling member can be mounted on the multi-chip module to constitute a unit, thereby facilitating the system configuration. Also, the refrigeration unit and the multi-chip module can be separated from each other by the coupler, so that the thermal and mechanical replacement is facilitated. Further, the use of the coupler with a refrigerant stopper makes the replacement possible conveniently without removing the refrigerant from inside the cooling member. Furthermore, if the cooling member is of the same size as the multi-chip module, and if clogged with a refrigerant, it can be handled with high maintainability by making the unit of such a weight as to be capable of being carried in hand.